Major 7.8 magnitude earthquake strikes off Indonesia Powerful earthquake strikes off coast of Sumatra island, triggering a tsunami warning which was later lifted. Indonesia has called off a tsunami warning after a a powerful and shallow 7.8 magnitude earthquake struck off the west coast of the island of Sumatra. The quake struck at a depth of 10 kilometres on Wednesday, triggering a tsunami alert for parts of Sumatra, including West Sumatra, North Sumatra and Aceh, the local BMKG quake monitoring agency said.